Etching Method

Abstract

To provide a method of preventing deterioration of a shape of a part of a silicon oxide film at etching, and etching a silicon nitride film at high accuracy with a high selection ratio against the silicon oxide film.SOLUTION: A etching method for performing dry etching a film structure having a silicon nitride film and a silicon oxide film previously formed onto a wafer arranged in a processing chamber in a state where a gas for a processing in the processing chamber is supplied without using a plasma, includes: a step of forming a reaction layer onto the silicon nitride film by being reacted to a hydrogen fluoride gas under 30°C or larger and 55°C or less as a first step; and a step of performing heating without flowing the hydrogen fluoride gas under 70°C or larger and 110°C or less as a second step after the first step, and removing the reaction layer formed in the first step by performing vaporization of them. By repeating the first and second steps at a plurality of times, the silicon nitride film is etched from an end part in a lateral direction.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present disclosure relates to an etching method, and more particularly to an isotropic dry etching process technology used in the process of removing silicon nitride films in semiconductor elements such as 3D memories. [Background technology]

[0002] Demands for lower power consumption and increased memory capacity are driving further miniaturization and three-dimensional device structures in semiconductor devices. In the manufacture of three-dimensional devices, due to their complex, three-dimensional structures, "isotropic etching," which allows for lateral etching, is increasingly used in addition to the conventional "vertical (anisotropic) etching," which involves etching perpendicular to the wafer surface. Traditionally, isotropic etching has been performed using wet processing with chemicals. However, with advances in miniaturization, problems have become apparent, such as pattern collapse due to the surface tension of the chemicals and etching residue in minute gaps. Furthermore, the need for large amounts of chemical processing is a problem. Therefore, it has become necessary to replace the conventional wet processing with dry processing, which does not require chemicals, for isotropic etching.

[0003] Silicon nitride films are widely used in semiconductor devices, and there are known examples of dry etching processes that use hydrogen fluoride (HF) gas but do not use plasma. For example, Patent Document 1 describes a method of etching a silicon nitride film without damaging a thermal oxide film by supplying hydrogen fluoride gas at a wafer temperature of 60°C or higher and 200°C or lower. Patent Document 2 also describes a method of selectively etching a silicon nitride film relative to a silicon oxide film by supplying hydrogen fluoride gas at a temperature of 10 to 120°C at a pressure of 1333 Pa or higher in a chamber.

[0004] As a known example of adding another component to HF gas, Patent Document 3 describes a method of selectively etching a silicon nitride film by supplying NO gas and / or ozone gas and HF gas, and Patent Document 4 describes a method of etching a silicon nitride film by contacting a mixed gas containing a fluorine-containing carboxylic acid and HF gas at less than 100°C without plasma.

[0005] As an example of etching using a fluorine-containing gas other than HF gas, Patent Document 5 discloses a method of selectively etching a silicon nitride film relative to a silicon oxide film using ClF gas. Patent Document 6 discloses a method of selectively etching a silicon nitride film using a fluorine-containing etching gas selected from the group consisting of FNO, FNO, FNO, and combinations thereof. Furthermore, Patent Document 7 discloses etching a silicon nitride film using an etching gas containing a halogen fluoride, which is a compound of bromine or iodine with fluorine, under a pressure of 1 Pa to 80 kPa without using plasma.

[0006] As an example of using radicals generated by some kind of plasma, Patent Document 8 describes a method in which a fluorine-containing gas, an alcohol gas, O2 gas, and an inert gas are supplied in a state excited by external plasma, thereby selectively etching a silicon nitride film relative to a silicon and / or silicon oxide film. Patent Document 9 also describes a method for selectively etching a silicon nitride film, which includes the steps of introducing a gas containing H and F and selectively introducing inert gas radicals into a processing space. Patent Document 10 also describes selective lateral etching of a silicon nitride film from a stacked structure of silicon nitride and silicon oxide films at temperatures below -20°C using a plasma-generated oxygen-containing precursor and a fluorine-containing precursor.

[0007] Furthermore, Patent Documents 6 and 10 describe selective lateral etching of a silicon nitride film from the sidewall of a high aspect ratio opening formed in a structure in which silicon nitride films and silicon oxide films are stacked in multiple layers in a 3D-NAND device, which is a 3D memory.

[0008] Furthermore, Patent Document 11 discloses that ammonium silicofluoride [(NH4)2SiF6], ammonium hydrogen fluoride [NH4HF2], and the like formed on a silicon nitride film can be removed by heating with a lamp or the like. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] Japanese Patent Application Laid-Open No. 2008-187105 [Patent Document 2] Japanese Patent Application Publication No. 2018-207088 [Patent Document 3] Japanese Patent Application Laid-Open No. 2014-197603 [Patent Document 4] Japanese Patent Application Publication No. 2019-091890 [Patent Document 5] Japanese Patent Application Laid-Open No. 2016-58544 [Patent Document 6] Special Publication No. 2021-509538 [Patent Document 7] International Publication No. 2021 / 079780 [Patent Document 8] Japanese Patent Application Laid-Open No. 2015-228433 [Patent Document 9] Japanese Patent Application Publication No. 2019-012759 [Patent Document 10] U.S. Patent No. 10,319,603 [Patent Document 11] Japanese Patent Application Laid-Open No. 2005-161493 Summary of the Invention [Problem to be solved by the invention]

[0010] For example, in the processing of stacked films for 3D-NAND flash memory, a three-dimensional semiconductor device, and around the gate of FinFET, technology is required to etch silicon nitride films isotropically and selectively with atomic layer control relative to polycrystalline silicon films and silicon oxide films. In particular, in the 3D-NAND structure, silicon oxide films (SiO2 films) and silicon nitride films (SiN) are alternately stacked in large numbers, and deep holes and grooves are formed in the layers, so a process is required to selectively and isotropically etch a small amount of silicon nitride film laterally.

[0011] As described in the background art, conventional wet etching using hydrofluoric acid solution or buffered hydrofluoric acid solution has problems such as remaining etching residue in minute gaps and poor etching controllability. Furthermore, dry etching has the problem of difficulty in etching silicon nitride film with high precision at a high selectivity relative to silicon oxide film, resulting in deterioration of the shape of the silicon oxide film portion that is desired to remain.

[0012] The present disclosure has been made in consideration of the above-mentioned problems, and provides an etching method that can highly selectively etch a silicon nitride film relative to a silicon oxide film with high precision without deteriorating the shape of the silicon oxide film that is desired to be left. [Means for solving the problem]

[0013] The etching method disclosed herein is an etching method for dry etching a film structure including a silicon nitride film and a silicon oxide film, which has been formed in advance on a wafer placed in a processing chamber, by supplying a processing gas into the processing chamber without using plasma. In the first step, hydrogen fluoride gas is reacted at a temperature of 30°C to 55°C to form a reaction layer on the silicon nitride film. After the first step, in the second step, heating is performed at a temperature of 70°C to 110°C without flowing hydrogen fluoride gas to volatilize and remove the reaction layer formed in the first step. The first and second steps are repeated multiple times to etch the silicon nitride film laterally from the edge. In the first and second steps, a stage on which the wafer is placed is set to a low temperature of -50°C to 0°C and the wafer placed on the stage is heated, thereby achieving a temperature of 30°C to 55°C in the first step and a temperature of 70°C to 110°C in the second step. [Effects of the Invention]

[0014] The above etching method can prevent the shape of the silicon oxide film from deteriorating during etching, and can provide a method for etching a silicon nitride film with high precision at a high selectivity relative to a silicon oxide film. Problems, configurations, and effects other than those described above will become clear from the description of the following embodiments. [Brief explanation of the drawings]

[0015] [Figure 1A] 10 is a graph showing the etching film thickness and selectivity of a silicon nitride film and a silicon oxide film relative to the output of an IR lamp irradiated simultaneously with the supply of HF in the first step according to the first embodiment (stage temperature -30°C, total pressure 300 Pa, 10 cycles). [Figure 1B] 10 is a graph showing the etching film thickness and selectivity of a silicon nitride film and a silicon oxide film relative to the output of an IR lamp irradiated simultaneously with the supply of HF in the first step according to the first embodiment (stage temperature -30°C, total pressure 600 Pa, 10 cycles). [Figure 1C]10 is a graph showing the etching film thickness and selectivity of a silicon nitride film and a silicon oxide film relative to the output of an IR lamp irradiated simultaneously with the supply of HF in the first step according to the first embodiment (stage temperature -30°C, total pressure 900 Pa, 10 cycles). [Figure 2A] 10 is a graph showing the etching film thickness and selectivity of a silicon nitride film and a silicon oxide film relative to the output of an IR lamp irradiated simultaneously with the supply of HF in the first step according to the second embodiment (stage temperature -20°C, total pressure 900 Pa, 10 cycles). [Figure 2B] 10 is a graph showing the etching film thickness and selectivity of a silicon nitride film and a silicon oxide film relative to the output of an IR lamp irradiated simultaneously with the supply of HF in the first step according to the second embodiment (stage temperature 0°C, total pressure 900 Pa, 10 cycles). [Figure 2C] 10 is a graph showing the etching film thickness and selectivity of a silicon nitride film and a silicon oxide film relative to the output of an IR lamp irradiated simultaneously with the supply of HF in the first step according to the second embodiment (stage temperature 20° C., total pressure 900 Pa, 10 cycles). [Figure 2D] 10 is a graph showing the etching film thickness and selectivity of a silicon nitride film and a silicon oxide film versus the irradiation time of an IR lamp used in the second step according to the second embodiment (stage temperature 0°C, total pressure 900 Pa, 10 cycles). [Figure 2E] 10 is a graph showing the thickness of a reaction layer on a silicon nitride film versus the number of cycles when the output of an IR lamp irradiated simultaneously with the supply of HF is changed in the first step according to the second embodiment. [Figure 3A] 10 is a graph showing the etching film thickness and selectivity of a silicon nitride film and a silicon oxide film when the stage temperature in the first step according to the third embodiment is changed. [Figure 3B] 10 is a graph showing the thickness of a reaction layer on a silicon nitride film versus the number of cycles when the stage temperature in the first step according to the third embodiment is changed. [Figure 4] 1 is a cross-sectional view showing an outline of an etching apparatus according to a first embodiment. [Figure 5]1 is a flow chart of a method for etching a silicon nitride film according to an embodiment. [Figure 6] 1 is a flow chart of a method for etching a silicon nitride film according to an embodiment. [Figure 7] 4 is a time chart schematically showing the flow of operations over time in the etching process according to the first embodiment. [Figure 8] 10 is a time chart schematically showing the flow of operations over time in an etching process according to a second embodiment. [Figure 9] 10 is a time chart schematically showing the flow of operations over time in an etching process according to a third embodiment. [Figure 10A] FIG. 2 is a partial cross-sectional view for explaining the progress of etching treatment of a stacked film of a silicon nitride film and a silicon oxide film (before etching) according to an example. [Figure 10B] FIG. 10 is a partial cross-sectional view for explaining the progress of etching treatment (after etching) of a stacked film of a silicon nitride film and a silicon oxide film according to an example. [Figure 11A] FIG. 10 is a partial cross-sectional view for explaining the progress of an etching process of a stacked film of a silicon nitride film and a silicon oxide film when the selectivity is poor in the example, in which the shape of the end of the silicon oxide film after etching is round instead of rectangular. [Figure 11B] 1 is a partial cross-sectional view for explaining the progress of etching of a stacked film of a silicon nitride film and a silicon oxide film according to an embodiment, in which the corners of the silicon oxide film are rounded to form triangles. [Figure 12] FIG. 10 is a partial cross-sectional view for explaining the progress of an etching process of a stacked film of a silicon nitride film and a silicon oxide film in an embodiment, in which the selectivity is relatively high, and the thickness of the silicon oxide film portion is reduced while the corners of the silicon oxide film maintain their rectangular shape. [Figure 13] FIG. 10 is a cross-sectional view showing an outline of an etching apparatus according to a second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0016] The present inventors have investigated etching using hydrogen fluoride gas (HF) without using plasma for single-layer silicon nitride films and silicon oxide films formed by plasma CVD (chemical vapor deposition).

[0017] Hereinafter, examples of the embodiment will be described in detail with reference to the drawings. [Example]

[0018] [Overall configuration of etching processing apparatus 1] First, an outline of the etching processing apparatus according to Example 1 will be described, including the overall configuration, with reference to FIG. 4. FIG. 4 is a cross-sectional view showing an outline of the etching apparatus according to the first embodiment. The etching processing apparatus 100 has a processing chamber 1. The processing chamber 1 is composed of a base chamber 11, and a wafer stage 3 for placing a wafer 2 thereon is installed therein. A shower plate 23 is installed in the center of the upper side of the processing chamber 1, and processing gas is supplied to the processing chamber 1 via the shower plate 23.

[0019] The supply flow rate of the process gas is adjusted by mass flow controllers 50 installed for each gas type. In addition, a gas distributor 51 is installed downstream of the mass flow controller 50, which allows the flow rate and composition of the gas supplied near the center of the process chamber 1 and the gas supplied near the periphery to be controlled independently, thereby enabling detailed control of the spatial distribution of the process gas partial pressure. Note that, although argon (Ar) gas, nitrogen (N2) gas, helium (He) gas, and hydrogen fluoride (HF) gas are shown in Figure 4 as examples, other process gases can also be supplied.

[0020] The lower part of the processing chamber 1 is connected to exhaust means 15 via vacuum exhaust piping 16 in order to reduce the pressure in the processing chamber 1. The exhaust means 15 is configured, for example, by a turbo molecular pump, a mechanical booster pump, or a dry pump. In addition, in order to adjust the pressure in the processing chamber 1, pressure adjustment means 14 is installed upstream of the exhaust means 15.

[0021] An IR lamp unit (infrared illumination unit) for heating the wafer 2 is installed above the wafer stage 3. The IR lamp unit mainly consists of an IR lamp 60, a reflector 61, and an IR light-transmitting window 72. A circular lamp is used as the IR lamp 60. Note that the light emitted from the IR lamp 60 is assumed to be light mainly ranging from visible light to infrared light (herein referred to as IR light). In this embodiment, three lamps 60-1, 60-2, and 60-3 are installed, but two or four lamps may be installed. A reflector 61 is installed above the IR lamp 60 to reflect the IR light downward (toward the placement of the wafer 2). The IR light-transmitting window 72 is preferably made of a material that does not contain alkali metal ions, transmits light in the infrared light range, and is heat-resistant; specifically, quartz is a preferred material.

[0022] An IR lamp power supply 73 is connected to the IR lamp 60, and a high frequency cut filter 74 is installed midway to prevent high frequency power noise from entering the IR lamp power supply 73. The IR lamp power supply 73 also has a function that enables the power supplied to the IR lamps 60-1, 60-2, and 60-3 to be controlled independently of one another, making it possible to adjust the radial distribution of the amount of heat applied to the wafer 2 (some of the wiring is not shown). A space is formed in the center of the IR lamp unit for installing a shower plate 23 for introducing process gases.

[0023] The wafer stage 3 has a coolant flow path 39 formed inside for cooling the stage, and the coolant is circulated and supplied by a chiller 38. In this embodiment, the chiller used for the wafer stage 3 is capable of temperature control from -50°C to 50°C, for example. The wafer stage 3 used here is a proximity cooling type.

[0024] Protrusions 56 are provided on the surface of the wafer stage 3, and the wafer 2 is mounted in a manner that it is supported at points by the protrusions 56. The height of the protrusions 56 is preferably, for example, approximately 0.1 mm to 1.0 mm, and the number of supporting points (i.e., the number of protrusions 56) is preferably three or more. Specifically, six protrusions 56 with a height of 0.25 mm were used here. The wafer stage 3 can be made of a corrosion-resistant metal or metal compound with high thermal conductivity.

[0025] Because there is a gap between the wafer stage 3 and the wafer 2 due to the protrusions 56, by flowing an inert gas such as He, Ar, or N2 throughout the chamber 11, the inert gas flows into the gap, causing heat conduction and cooling the wafer 2. Note that the electrostatic adsorption method shown in Example 2 can also be used to cool the wafer 2.

[0026] Furthermore, a thermocouple 70 for measuring the temperature of the wafer stage 3 is installed inside the wafer stage 3, and the thermocouple 70 is connected to a thermocouple thermometer 71. The temperature of the stage 3 measured by the thermocouple 70 and the thermocouple thermometer 71 was within ±1°C of the set temperature of the chiller 38.

[0027] The proximity cooling stage 3 described above has the advantage of being simple in structure, allowing for low costs. However, when the chamber 11 is idle and in a vacuum state, the wafer 2 is insulated, so it takes a certain amount of time for inert gas to flow and cooling to begin. In addition, because the distance between the coolant from the chiller 38 and the wafer 2 is relatively long, it was found that the actual temperature of the wafer 2 tends to be higher than the set temperature of the chiller 38. When the temperature during cooling and processing was measured using a wafer with a thermocouple attached, it was found that the actual temperature of the wafer 2 was approximately 5°C higher than the set temperature of the chiller 38.

[0028] As a mechanism for cooling the stage 3 used in the etching processing apparatus 100 of this embodiment, a Peltier element, which is a thermoelectric conversion device, or the like can also be used in addition to a mechanism for circulating a coolant.

[0029] The etching processing apparatus 100 used in this embodiment can heat the inside of the chamber 11 other than the wafer stage 3 that is exposed to hydrogen fluoride gas, such as the processing chamber 1. For example, a temperature of about 40°C to 120°C can be used. This makes it possible to prevent hydrogen fluoride gas and the like from being adsorbed inside the chamber 11, and to minimize corrosion inside the chamber 11.

[0030] In this embodiment, HF is used at a pressure of, for example, 50 Pa to 1000 Pa (50 Pa or more and 1000 Pa or less), with the stage temperature of the stage 3 set to 40°C to -30°C. Depending on the stage temperature of the stage 3, it is thought that HF ​​may aggregate and liquefy on the silicon nitride film. Therefore, when using an electrostatic chucking method, if solidification or liquefaction occurs on the backside of the wafer 2, the seal band for the backside cooling gas of the wafer 2 may break, causing leakage of cooling gas such as He, which may result in an electrostatic chuck error. In contrast, the proximity-cooled stage 3 shown in FIG. 4 has a gap between the wafer stage 3 and the wafer 2 due to the protrusion 56, so even if HF solidifies or liquefies, no error occurs in the wafer stage 3, enabling stable processing.

[0031] Furthermore, with the electrostatic chuck method, because the gap between wafer 2 and stage 3 is narrow, wafer 2 tends to stick to stage 3 due to surface tension when HF liquefies. As a result, when dechucking wafer 2, lifting wafer 2 with a pusher pin can cause the wafer 2 to crack. To address this issue, we adopted a proximity cooling method with a 0.25 mm gap between wafer 2 and stage 3, which mitigated the problem of wafer 2 sticking to stage 3 when HF liquefies.

[0032] In the application of a process using low temperatures, as in the present embodiment, condensation may occur on components inside the electrostatic chuck electrode, which serves as a cooling source, that come into contact with the atmosphere, potentially causing a short circuit in an electrical circuit such as a power supply unit. In this respect, the structure of the stage 3 with proximity cooling, which simplifies the components inside the electrode, is advantageous.

[0033] [Etching method: Dry etching process flow] Next, the flow of the dry etching process using hydrogen fluoride gas without using plasma proposed in this embodiment will be explained using Figures 4, 5, and 7. Figure 5 is a flow chart of the etching method for silicon nitride film according to the embodiment. Figure 7 is a time chart that schematically shows the flow of operations over time in the etching process according to the first example.

[0034] First, the wafer 2 is transferred into the processing chamber 1 through a transfer port (not shown) provided in the processing chamber 1, and then the wafer 2 is placed (mounted) on the protrusion 56 on the wafer stage 3.

[0035] Thereafter, Ar gas for wafer cooling is supplied to the wafer 2 via the mass flow controller 52, the gas distributor 51, and the shower plate 23, thereby performing wafer cooling in step S101 of FIG. 5. Because the Ar gas serves both as a heat transfer gas to the wafer 2 and as a dilution gas for diluting the HF gas, steps S101 and S102 of FIG. 5 are performed simultaneously. The flow rate of the Ar gas can be changed (different flow rates can be used) when cooling the wafer 2 and when used as a dilution gas. The flow of the dilution Ar gas can be continued or stopped until the etching process is completed. Instead of Ar gas, N2 gas can be used as an inert gas.

[0036] Next, in step S103 of FIG. 5 , a predetermined amount of HF gas was supplied to the processing chamber 1 for a predetermined time. At the same time, the wafer 2 was heated to form a reaction layer on the wafer 2. Here, heating was performed using an IR (infrared) lamp 60. The wafer temperature of the wafer 2 obtained as a result of cooling by the stage 3 and heating by the IR lamp 60 is preferably, for example, 30°C to 55°C, more preferably 35°C to 50°C. As described in the examples below, which vary the conditions, the total pressure or HF partial pressure, the heating temperature (here, the output of the IR lamp 60), the heating time, the number of repetitions, and other factors can control the reaction layer thickness. Furthermore, if the wafer temperature of the wafer 2 is lower than, for example, 30°C, the reaction layer is not sufficiently formed, and etching is difficult to occur. Conversely, if the wafer temperature of the wafer 2 is higher than, for example, 55°C, an excessive reaction layer may be formed. Therefore, when the excessive reaction layer is decomposed and volatilized, the adjacent silicon oxide film is undesirably etched, reducing the etching selectivity.

[0037] In this embodiment, the pressure used is preferably, for example, about 10 Pa to 1000 Pa, more preferably 50 Pa to 1000 Pa (50 Pa or more and 1000 Pa or less), and particularly preferably 100 Pa to 1000 Pa. The higher the pressure, the easier it is to form a reaction layer on the silicon nitride film, and the lower the temperature required for formation. Even when the pressure is increased, by controlling the output of the IR lamp 60, it is possible to form a reaction layer on the silicon nitride film without affecting the silicon oxide film.

[0038] After forming the reaction layer for a predetermined time, in step S104 of Fig. 5, the supply of HF gas is stopped, and exhaust means 15 is used to exhaust the HF gas remaining in the gas phase and the reaction products on the silicon nitride film as the reaction layer. When performing vacuum exhaust, it is desirable to set the pressure to, for example, 5 Pa or less. In step S104, the reaction products can be more efficiently exhausted by supplying Ar gas as a diluent gas during and after the exhaust. When exhausting while flowing Ar, it is desirable to set the pressure to, for example, 40 Pa or less.

[0039] Next, heating is performed without flowing HF gas to remove the reaction layer (step S105 in FIG. 5). The heating temperature here is preferably, for example, 70 to 110°C (70 to 110°C), more preferably 70 to 100°C (70 to 100°C). Here, IR lamps 60 are used as the heating method. The heating method is not limited to this. For example, a method of heating the wafer stage 3 or a method of transferring the wafer 2 to a heating-only device and performing a heat treatment thereon may also be used. Furthermore, Ar gas or nitrogen gas may be introduced into the processing chamber 1 during irradiation with the IR lamps 60. Furthermore, the heat treatment may be performed multiple times as needed. After heating, the wafer is cooled in step S106. Thereafter, steps S102 to S106 constitute one cycle, and this cycle is repeated N times (N is a positive integer). After repeating the cycle until the required etching depth is obtained, the etching method of FIG. 4 is completed.

[0040] Fig. 7 shows a time chart of the etching method flow shown in Fig. 5. One cycle includes a step of heating with the IR lamp 60 while flowing HF gas (step S103) and a step of heating with the IR lamp 60 without flowing HF gas (step S105), and by repeating this process N times, the silicon nitride film is etched.

[0041] [Etching result 1] The results of etching using hydrogen fluoride (HF) gas without using plasma according to this embodiment are shown below. The temperature of stage 3 was set to -30°C, and the etching rates of single-layer silicon nitride (PE-SiN) and silicon oxide (PE-SiO2) films formed by plasma CVD were measured.

[0042] Here, the base wafer 2 used was a high resistance substrate (31 Ωcm) with a diameter of 300 mm, on which 2 cm square coupon samples of silicon nitride film and silicon oxide film were attached with silicone vacuum grease.

[0043] The wafer 2 was placed in the processing chamber 1 of the etching processing apparatus 100 shown in FIG. 4, and then etched using the process flow of the etching method shown in FIG. 5. First, to cool the wafer, Ar was flowed at a flow rate of 1.4 L / min at 900 Pa for 60 seconds. After that, the pressure was adjusted to the set value, and HF was introduced at a flow rate of 0.40 L / min and Ar as a diluent gas at a flow rate of 0.20 L / min, while simultaneously irradiating with the IR lamp 60 at a predetermined output. Here, the time for HF introduction and IR irradiation was set to 60 seconds. This resulted in the formation of a reaction layer on the silicon nitride film.

[0044] Thereafter, the pressure adjusting means 14 was fully opened and the wafer 2 was evacuated for 120 seconds. This exhaust operation evacuated the fluorine gas and some of the reaction products. Next, with the set temperature of the stage 3 unchanged and Ar flowing at a flow rate of 0.50 L / min, the IR lamp 60 was heated at a predetermined lamp intensity for 30 to 50 seconds with the exhaust valve in the pressure adjusting means 14 fully opened. This removes the reaction layer. After that, the wafer 2 was cooled by flowing Ar at a pressure of 900 Pa and a flow rate of 1.4 L / min for 60 seconds, returning to the beginning. This series of processes (steps S102 to S106) was repeated 10 times in accordance with the flow chart of FIG. 5.

[0045] 1A, 1B, and 1C show the etched film thickness of a silicon nitride film (PE-SiN), the etched film thickness of a silicon oxide film (PE-SiO2), and the selectivity of a silicon nitride film to a silicon oxide film obtained after 10 cycles when the output of the IR lamp 60 was changed. FIG. 1A is a graph showing the etched film thickness and selectivity of a silicon nitride film and a silicon oxide film versus the output of the IR lamp irradiated simultaneously with the HF supply in the first step of the first embodiment (stage temperature -30°C, total pressure 300 Pa, 10 cycles). FIG. 1B is a graph showing the etched film thickness and selectivity of a silicon nitride film and a silicon oxide film versus the output of the IR lamp irradiated simultaneously with the HF supply in the first step of the first embodiment (stage temperature -30°C, total pressure 600 Pa, 10 cycles). FIG. 1C is a graph showing the etching film thickness and selectivity of silicon nitride and silicon oxide films versus the output of the IR lamp irradiated simultaneously with the HF supply in the first step according to the first embodiment (stage temperature -30°C, total pressure 900 Pa, 10 cycles). Here, FIGS. 1A, 1B, and 1C show the results of experiments in which the pressure during HF / Ar introduction and IR irradiation was changed to 300 Pa, 600 Pa, and 900 Pa, respectively. The IR lamp irradiation to remove the reaction layer formed in the second step (S103) was performed for 50 seconds at an output of 70%.

[0046] As shown in Figure 1A, when using 300 Pa and an IR output of 60% or more, an etching amount of about 15 nm of the silicon nitride film (PE-SiN) was obtained in 10 cycles. However, at an IR output of 65% or more, etching of the silicon oxide film (PE-SiO2) also began to occur, and the selectivity was found to deteriorate.

[0047] As shown in Figure 1B, when the pressure was increased to 600 Pa, the etching amount of the silicon nitride film (PE-SiN) increased in proportion to the IR lamp output. By increasing the pressure, the etching amount of the silicon nitride film (PE-SiN) increased overall, and the selectivity relative to the silicon oxide film (PE-SiO2) also increased. However, even in this case, etching of the silicon oxide film (PE-SiO2) began to occur at IR output of 65% or more. Furthermore, as shown in Figure 1C, when the pressure was increased to 900 Pa, the etching amount of the silicon nitride film (PE-SiN) tended to increase as the IR output increased, and the etching amount was found to increase further.

[0048] Using Wafer 2 equipped with a thermocouple, the HF gas was replaced with Ar, and the process temperature during lamp irradiation was actually measured. Table 1A shows the IR lamp output (IR output: 50%, 55%, 60%, 65%) when the stage temperature was -30°C, and the temperature of Wafer 2 after 60 seconds. The temperatures shown here are those reached. Like the base wafer, a high-resistivity substrate was used. The measured temperatures were between 30°C and 57°C. Temperature measurements were also performed during the process of removing the reaction layer, and it was found that the temperature reached was 80°C.

[0049] [Table 1A]

[0050] The structure of the film targeted by this embodiment will be described with reference to FIGS. 10A and 10B. FIG. 10A is a partial cross-sectional view illustrating the progress of an etching process (before etching) on ​​a stacked film of a silicon nitride film and a silicon oxide film according to an embodiment. FIG. 10B is a partial cross-sectional view illustrating the progress of an etching process (after etching) on ​​a stacked film of a silicon nitride film and a silicon oxide film according to an embodiment. The structure of the film targeted by this embodiment is a structure required for 3D-NAND, in which multiple silicon nitride films 103 and silicon oxide films 102 are alternately stacked on a substrate 101 as shown in FIG. 10A, and deep hole or trench shapes are formed as openings 104 therein. That is, this configuration is a film structure in which the edges of the stacked film layers, in which the silicon nitride films are sandwiched between silicon oxide films above and below, form the sidewalls of the trenches or holes. The thickness of the silicon nitride film 103 used here is several nanometers to 100 nm, and the thickness of the silicon oxide film 102 is several nanometers to 100 nm. Furthermore, these layers are stacked in tens to hundreds of layers. The total thickness 105 of these stacked layers is several μm to several tens of μm. The width of the opening 104 is several tens of nm to several hundreds of nm. By the process of this embodiment, the silicon nitride film 103 is etched laterally with high selectivity to the silicon nitride film 102, as shown in FIG. 10B. The dimension 106 of this lateral etching is several nm to several tens of nm.

[0051] 11A, 11B, and 12 are diagrams illustrating examples of the shape of the end of the silicon oxide film 102 after etching. FIG. 11A is a partial cross-sectional view illustrating the progress of an etching process on a stacked film of a silicon nitride film and a silicon oxide film when the selectivity is poor according to an embodiment, in which the end shape of the silicon oxide film after etching is round rather than rectangular. FIG. 11B is a partial cross-sectional view illustrating the progress of an etching process on a stacked film of a silicon nitride film and a silicon oxide film according to an embodiment, in which the corners of the silicon oxide film have been rounded to form triangles. FIG. 12 is a partial cross-sectional view illustrating the progress of an etching process on a stacked film of a silicon nitride film and a silicon oxide film according to an embodiment, in which the selectivity is relatively high, in which the corners of the silicon oxide film remain rectangular while the thickness of the silicon oxide film portion has become thinner.

[0052] Here, when etching the silicon nitride film 103 in the lateral direction, the selectivity to the silicon oxide film 102 is preferably 10 or more, more preferably 20 or more. If this selectivity is low, etching of the silicon oxide film 102, which should not be etched, occurs at the same time, and the shape of the edge of the silicon oxide film 102 after etching becomes rounded rather than rectangular, as shown by 111 in FIG. 11A, which adversely affects device performance.

[0053] Empirically, a shape closer to a rectangle as shown in Fig. 10B can be obtained when the selectivity is 10 or more, more preferably 20 or more. On the other hand, when the selectivity is less than 5, the shape of the edge of the silicon oxide film 102 becomes rounded as shown by 111 in Fig. 11A, which is not desirable.

[0054] Here, the etching characteristics of fine patterns were evaluated using a sample in which a total of 20 layers of silicon nitride film 103 (40 nm thick) and silicon oxide film 102 (40 nm thick) were alternately formed, with 200 nm slit-shaped spaces (openings 104) formed. Ten cycles of etching were performed under the experimental conditions shown in Figures 1A, 1B, and 1C. The results are shown in Tables 1B, 1C, and 1D. Table 1B shows the etching results at a stage temperature of -30°C and 300 Pa. Table 1C shows the etching results at a stage temperature of -30°C and 600 Pa. Table 1D shows the etching results at a stage temperature of -30°C and 900 Pa. Table 1E shows the symbols and criteria for the evaluation results of the slit sample.

[0055] As a result, as shown in FIG. 10B, when etching of the silicon nitride film 103 proceeds with high selectivity and results in a nearly rectangular shape, as shown in FIG. 11A, the selectivity is poor, resulting in rounded edges of the silicon oxide film 102 that should remain (indicated by 111). Even when the selectivity is relatively good, the corners of the silicon oxide film 102 are sometimes rounded and triangular (indicated by 113) as shown in FIG. 11B. Furthermore, even when the corners of the silicon oxide film 102 remain rectangular, the thickness of the tip of the silicon oxide film 102 is sometimes thin (indicated by 112) as shown in FIG. 12. 112 in FIG. 12 shows an example of the edge of the silicon oxide film 102 after etching, where the corners of the silicon oxide film 102 remain rectangular but the thickness of the silicon oxide film 102 is thin. 113 in FIG. 11B shows an example of the edge of the silicon oxide film 102 after etching, where the corners of the silicon oxide film 102 are rounded and triangular. The composition formula of the silicon oxide film is expressed as SiO2 or SiO2.

[0056] Therefore, Tables 1B, 1C, and 1D show the recess amount (the amount of silicon nitride film etched minus the amount of silicon oxide film etched), the selectivity from the slit pattern results (the amount of silicon nitride film etched from its initial dimensions divided by the amount of silicon oxide film etched), and the remaining SiO2 thickness (thickness 108 of the tip of silicon oxide film 102 after etching shown in FIG. 12 divided by thickness 107 of initial silicon oxide film 102). Good etching conditions here are those in which the recess amount is relatively large, the selectivity is large, and the remaining SiO2 thickness is close to 1.

[0057] To make the evaluation results easier to understand, symbols such as ◎, 〇, △, and × are also listed in Tables 1B, 1C, and 1D. The criteria for these are shown in Table 1E.

[0058] [Table 1B]

[0059] [Table 1C]

[0060] [Table 1D]

[0061] [Table 1E]

[0062] As shown in Tables 1B, 1C, and 1D, in all cases, when the IR lamp output (IR output) was high, the remaining SiO2 thickness became small, and it was found that this was not a suitable condition. Therefore, it was found that the remaining SiO2 thickness may be low even when the selectivity is relatively high. From the above, it was found that the temperature required to satisfy the recess depth, selectivity, and remaining SiO2 thickness was between 30°C and 55°C.

[0063] In addition, high temperature and high pressure contribute to increasing the etching amount of the silicon nitride film 103, but as the temperature increases, the remaining SiO2 thickness decreases, so it was found that the characteristics are better when the pressure is increased and the temperature is lowered. [Example]

[0064] [Etching treatment device 2] Next, an outline of an etching processing apparatus 200 according to Example 2 of this embodiment, including its overall configuration, will be described with reference to FIG. 13 . FIG. 13 is a cross-sectional view showing an outline of the etching apparatus according to Example 2. The etching processing apparatus 200 includes a processing chamber 1. The processing chamber 1 is composed of a base chamber 11, which contains a wafer stage 3 for supporting a wafer 2. A plasma source is installed above the processing chamber 1 and uses an ICP discharge method. The ICP plasma source can be used to clean the inner walls of the chamber 11 using plasma or to generate reactive gases using plasma. A cylindrical quartz chamber 12 constituting the ICP plasma source is installed above the processing chamber 1, and an ICP coil 20 is installed outside the quartz chamber 12. A high-frequency power source 21 for generating plasma is connected to the ICP coil 20 via a matching device 22. The high-frequency power generated by the high-frequency power source 21 has a frequency band of several tens of megahertz, such as 13.56 MHz. A top plate 25 is installed above the quartz chamber 12. A gas dispersion plate 24 and a shower plate 23 are installed below the top plate 25 , and the processing gas is introduced into the quartz chamber 12 via the gas dispersion plate 24 and the shower plate 23 .

[0065] The supply flow rate of the process gas is adjusted by mass flow controllers 50 installed for each gas type. In addition, a gas distributor 51 is installed downstream of the mass flow controller 50, and the gas distributor 51 independently controls the flow rate and composition of the gas supplied near the center of the quartz chamber 12 and the gas supplied near the periphery, allowing for detailed control of the spatial distribution of the process gas partial pressure. Note that although Ar, N2, HF, and O2 are shown as process gases in Figure 13, other gases can also be supplied as needed.

[0066] An exhaust means 15 is connected to the bottom of the processing chamber 1 via a vacuum exhaust pipe 16 in order to reduce the pressure in the processing chamber. The exhaust means 15 is configured, for example, by a turbo molecular pump, a mechanical booster pump, or a dry pump. In addition, a pressure adjustment means 14 is installed upstream of the exhaust means 15 in order to adjust the pressure in the processing chamber 1.

[0067] An IR lamp unit for heating the wafer 2 is installed above the wafer stage 3. The IR lamp unit mainly consists of an IR lamp 60, a reflector 61, and an IR light-transmitting window 72. A circular lamp is used as the IR lamp 60. The light emitted from the IR lamp is assumed to be light mainly ranging from visible light to infrared light (herein referred to as IR light). In this embodiment, three lamps 60-1, 60-2, and 60-3 are installed, but two or four lamps may be installed. A reflector 61 is installed above the IR lamp 60 to reflect the IR light downward (toward the wafer placement direction). The IR light-transmitting window 72 is preferably made of a material that does not contain alkali metal ions, transmits light in the infrared light range, and is heat-resistant; specifically, quartz is a preferred material.

[0068] An IR lamp power supply 73 is connected to the IR lamp 60, and a high frequency cut filter 74 is installed midway to prevent high frequency power noise from entering the IR lamp power supply 73. The IR lamp power supply 73 is also equipped with a function that enables the power supplied to the IR lamps 60-1, 60-2, and 60-3 to be controlled independently of one another, making it possible to adjust the radial distribution of the amount of heat applied to the wafer 2 (some of the wiring is not shown).

[0069] A flow path 27 is formed in the center of the IR lamp unit. A slit plate 26 with multiple holes is installed in this flow path 27 to block ions and electrons generated in the plasma and allow only neutral gases and neutral radicals to pass through and irradiate the wafer 2. The material of the slit plate 26 is preferably heat-resistant and does not contain alkali metal ions, and specific examples of such materials include alumina and quartz.

[0070] The wafer stage 3 has a coolant flow path 39 formed therein for cooling the stage, and the coolant is circulated and supplied by a chiller 38. In this embodiment, a chiller 38 capable of controlling the temperature of the wafer stage 3 between -50°C and 50°C is used. Furthermore, to fix the wafer 2 by electrostatic adsorption, plate-shaped electrode plates 30 are embedded in the stage 3, and a DC power supply 31 is connected to each of the electrode plates 30. Furthermore, to efficiently cool the wafer 2, He gas can be supplied between the backside of the wafer 2 and the wafer stage 3. Furthermore, to prevent damage to the backside of the wafer 2 even when heating and cooling are performed while the wafer 2 is adsorbed, the surface of the wafer stage 3 (the surface on which the wafer 2 is placed) is coated with a resin such as polyimide. Furthermore, a thermocouple 70 for measuring the temperature of the stage 3 is installed inside the wafer stage 3, and the thermocouple 70 is connected to a thermocouple thermometer 71.

[0071] The temperature of stage 3 measured by thermocouple thermometer 71 using thermocouple 70 was within ±1°C of the set temperature of chiller 38, and the temperature of wafer 2 measured separately by thermocouple 70 was within ±3°C (within ±2°C of the temperature of stage 3).

[0072] As a mechanism for cooling the stage 3 used in the etching processing apparatus 200 of this embodiment, a Peltier element, which is a thermoelectric conversion device, or the like can also be used in addition to a mechanism for circulating a coolant.

[0073] Furthermore, the etching processing apparatus 200 used in this embodiment can heat the inside of the chamber 11 other than the wafer stage 3 that is exposed to hydrogen fluoride gas, such as the processing chamber 1. For example, a temperature of about 40°C to 120°C can be used. This makes it possible to prevent hydrogen fluoride gas from being adsorbed inside the chamber 11, and to minimize corrosion inside the chamber.

[0074] [Etching method: Dry etching process flow 2] Next, the flow of the etching process using hydrogen fluoride gas without using plasma proposed in this embodiment will be explained using Figures 5, 8, and 13 (apparatus diagrams). Figure 5 is a flow chart of the etching method for silicon nitride film according to the embodiment. Figure 8 is a time chart that schematically shows the flow of operations over time in the etching process according to the second example.

[0075] First, the wafer 2 is transferred into the processing chamber 1 through a transfer port (not shown) provided in the processing chamber 1, and then the wafer 2 is fixed to the wafer stage 3 by a DC power supply 31 for electrostatic adsorption, and He gas 55 for wafer cooling is supplied to the backside of the wafer 2, thereby performing wafer cooling in step S101 of Fig. 5. A valve 54 is provided between the He gas 55 and the vacuum exhaust pipe 16.

[0076] 5, Ar gas for diluting the HF gas is supplied to the processing chamber 1 via the mass flow controller 50, the gas distributor 51, and the shower plate 23. The Ar gas for dilution can be continued to flow until the etching process is completed, or can be stopped. Also, N gas can be used as an inert gas instead of Ar gas.

[0077] 5, a predetermined amount of HF gas was supplied as a processing gas for a predetermined time into the processing chamber 1, and simultaneously, heating was performed to form a reaction layer. Here, heating by IR (infrared) lamps 60 was used as the heating method. The temperature of the wafer 2 obtained as a result of cooling by the stage 3 and heating by the IR lamps 60 is preferably, for example, 30°C or higher and 55°C or lower, and more preferably 35°C or higher and 50°C or lower. As will be described in examples using different conditions below, the film thickness of the reaction layer can be controlled by the total pressure or HF partial pressure, the heating temperature, the lamp output of the IR lamps 60 in this case, the time, the number of repetitions, and the like.

[0078] In this embodiment, the pressure used is preferably, for example, about 10 Pa to 1000 Pa, more preferably 50 Pa to 1000 Pa (50 Pa or more and 1000 Pa or less), and particularly preferably 100 Pa to 1000 Pa. The higher the pressure, the easier it is to form a reaction layer on the silicon nitride film 103, and the lower the temperature required for formation. Even when the pressure is increased, by controlling the output of the IR lamp 60, it is possible to form a reaction layer on the silicon nitride film 103 without affecting the silicon oxide film 102.

[0079] 5, after forming the reaction layer for a predetermined time, the supply of HF gas is stopped and the HF gas remaining in the gas phase and the reaction products on the silicon nitride film 103 as the reaction layer are exhausted. In step S104, Ar gas as a diluent gas is supplied during and after the exhaust, so that the reaction products can be exhausted more efficiently.

[0080] Next, heating is performed without flowing HF gas to remove the reaction layer (step S105 in FIG. 5). The heating temperature here is preferably, for example, 70 to 110°C (70 to 110°C), more preferably 70 to 100°C (70 to 100°C). Here, IR lamps 60 are used as the heating method. The heating method is not limited to this. For example, a method of heating the wafer stage 3 or a method of transferring the wafer 2 to a heating-only device and performing a heating process thereon may also be used. Ar gas or nitrogen gas may be introduced during irradiation with the IR lamps 60. The heating process may also be performed multiple times as needed. After heating, the wafer is cooled in step S106. Steps S102 to S106 constitute one cycle, and this cycle is repeated N times (N is a positive integer). The cycle is repeated until the required etching depth is obtained, and then the etching method is completed.

[0081] Fig. 8 shows a time chart for the flow shown in Fig. 5. One cycle consists of a step of performing IR lamp heating while flowing HF gas (step S103) and a step of performing IR lamp heating without flowing HF gas (step S105), and this cycle is repeated N times to etch the silicon nitride film.

[0082] [Etching result 2] Etching was performed under various conditions using the etching processing apparatus 200 shown in FIG. 13 and the process flows shown in FIGS. 5 and 8. In Example 1, the flow rates were fixed at HF / Ar = 0.40 / 0.20 (L / min), the stage temperature was fixed at −30°C, and the total pressure was varied between 300 Pa, 600 Pa, and 900 Pa. In Example 2, the total pressure was fixed at 900 Pa, the HF and Ar flow rates were kept constant, and the stage temperature of stage 3 was varied between −20°C, 0°C, and 20°C. Similar to Example 1, etching was performed using hydrogen fluoride gas without plasma, as in Example 1. During etching, a voltage of, for example, ±1200 V was applied to electrostatically adsorb the wafer 2 to the stage 3. To improve the thermal conductivity of the stage 3, He was flowed from the backside of the wafer 2 at a pressure of, for example, 1.0 kPa.

[0083] After Ar was introduced at a flow rate of 1.0 L / min and the pressure was set to 900 Pa, HF was introduced at a flow rate of 0.40 L / min and Ar as a diluent gas at a flow rate of 0.20 L / min, while simultaneously irradiating with the IR lamp 60 at a predetermined output. Here, the time for HF introduction and IR irradiation was set to 60 seconds. As a result, a reaction layer was formed on the silicon nitride film 103.

[0084] Thereafter, the exhaust valve in the pressure adjusting means 14 was opened 100% and the chamber was evacuated for 120 seconds. This exhaust operation evacuated the fluorine gas and some of the reaction products. Next, with the set temperature of stage 3 unchanged and Ar flowing at a flow rate of 0.50 L / min, the IR lamp 60 was heated at a predetermined lamp intensity for 30 to 50 seconds with the exhaust valve in the pressure adjusting means 14 opened 100%. This removes the reaction layer. After that, the chamber returned to the beginning and cooled while Ar was flowing at a pressure of 900 Pa and a flow rate of 1.4 L / min for 60 seconds. This series of processes (steps S102 to S106) was repeated 10 times in accordance with the flow chart of FIG. 5.

[0085] 2A, 2B, and 2C show the etched thickness of a silicon nitride film (PE-SiN), the etched thickness of a silicon oxide film (PE-SiO2), and the selectivity of a silicon nitride film to a silicon oxide film obtained after 10 cycles when the output of the IR lamp 60 was changed. FIG. 2A is a graph showing the etched thickness and selectivity of a silicon nitride film and a silicon oxide film versus the output of the IR lamp irradiated simultaneously with the HF supply in the first step of the second embodiment (stage temperature -20°C, total pressure 900 Pa, 10 cycles). FIG. 2B is a graph showing the etched thickness and selectivity of a silicon nitride film and a silicon oxide film versus the output of the IR lamp irradiated simultaneously with the HF supply in the first step of the second embodiment (stage temperature 0°C, total pressure 900 Pa, 10 cycles). 2C is a graph showing the etching film thickness and selectivity of silicon nitride and silicon oxide films versus the output of the IR lamp irradiated simultaneously with HF supply in the first step of the second embodiment (stage temperature 20°C, total pressure 900 Pa, 10 cycles). Figures 2A, 2B, and 2C show the results of an experiment in which the temperature of stage 3 was changed to -20°C, 0°C, and 20°C, respectively. The IR lamp 60 used to remove the reaction layer was irradiated for 40 seconds at 70% output.

[0086] Using wafer 2 equipped with a thermocouple, the HF gas was replaced with Ar, and the process temperature during lamp irradiation was actually measured. Table 2A shows the IR lamp output (IR output) and the temperature after 60 seconds when the stage temperature was different. Table 2B shows the temperature after 40 seconds with the IR lamp output at 70%. As shown in Table 2A, the temperatures reached were found to be between 21°C and 81°C. Temperature measurements were also performed during the process of removing the reaction layer, and the temperatures reached were found to be those shown in Table 2B.

[0087] [Table 2A]

[0088] [Table 2B]

[0089] 2A, 2B, and 2C, it is clear that the greater the output (IR output) of the IR lamp 60, the greater the etched film thickness of the silicon nitride film (PE-SiN). Furthermore, as the temperature of stage 3 increases, the graph of the etching amount of the silicon nitride film (PE-SiN) shifts to the left, indicating that the same etching amount can be obtained with a lower output (IR output) of the IR lamp 60. However, when the temperature of stage 3 is high, the etching amount of the silicon oxide film (PE-SiO2) tends to increase when the output of the IR lamp 60 is high, indicating a decrease in selectivity.

[0090] Here, when etching the silicon nitride film 103 in the lateral direction, the selectivity to the silicon oxide film 102 is preferably 10 or more, more preferably 20 or more. If this selectivity is low, etching of the silicon oxide film 102, which should not be etched, occurs at the same time, and the shape of the edge of the silicon oxide film 102 after etching becomes rounded rather than rectangular, as shown by 111 in FIG. 11A, which adversely affects device performance.

[0091] Empirically, a shape closer to a rectangle as shown in Fig. 10B can be obtained when the selectivity is 10 or more, more preferably 20 or more. On the other hand, when the selectivity is less than 5, the shape of the edge of the silicon oxide film 102 becomes rounded as shown by 111 in Fig. 11A, which is not desirable.

[0092] Here, similar to Example 1, a sample was formed with 20 layers of silicon nitride film 103 (40 nm thick) and silicon oxide film 102 (40 nm thick) alternately deposited for a total of 20 times, and a sample with 200 nm slit-shaped spaces formed therein was used to evaluate the etching characteristics of a fine pattern. The experimental conditions were the same as those used in Figures 2A, 2B, and 2C, and the slit sample was etched for 10 cycles. The results are shown in Tables 2C, 2D, and 2E. Table 2C shows the etching results at a stage temperature of -20°C and 900 Pa. Table 2D shows the etching results at a stage temperature of 0°C and 900 Pa. Table 2E shows the etching results at a stage temperature of 20°C and 900 Pa.

[0093] As a result, when etching proceeds with high selectivity and in a nearly rectangular shape, as shown in Figure 10B, the selectivity is poor and the edges of the silicon oxide film that should remain are sometimes rounded, as shown in Figure 11A. Even when the selectivity is relatively good, the corners of the silicon oxide film are sometimes rounded and triangular, as shown in Figure 11B. Furthermore, even when the corners of the silicon oxide film remain rectangular, as shown in Figure 12, the thickness of the silicon oxide film portion becomes thin.

[0094] Therefore, Tables 2C, 2D, and 2E show the recess amount (the amount of silicon nitride film etched minus the amount of silicon oxide film etched), the selectivity from the slit pattern results (the amount of silicon nitride film etched from the initial dimensions divided by the amount of silicon oxide film etched), and the remaining SiO2 thickness (the thickness 108 of the tip of the silicon oxide film after etching shown in Figure 12 divided by the initial silicon oxide film thickness 107). Good etching conditions here are those where the recess amount is relatively large, the selectivity is large, and the remaining SiO2 thickness is close to 1.

[0095] To make the evaluation results easier to understand, symbols such as ◎, 〇, △, and × are also shown in Tables 2C, 2D, and 2E. The criteria are as shown in Table 1E above.

[0096] [Table 2C]

[0097] [Table 2D]

[0098] [Table 2E]

[0099] As shown in Tables 2C, 2D, and 2E, the appropriate IR lamp 60 output is smaller when the stage temperature is higher. Furthermore, in all cases, it was found that high IR lamp 60 output results in a smaller residual SiO2 thickness, making these conditions unsuitable. Therefore, it was found that even when the selectivity is relatively high, the residual SiO2 thickness can be low. Naturally, the selectivity was also poor when the IR output was too low, as in the case of a stage temperature of -20°C and an IR output of 45%. From the above, it was found that the temperature required to satisfy the recess depth, selectivity, and residual SiO2 thickness was between 30°C and 55°C.

[0100] Furthermore, when the residual SiO2 thicknesses in Tables 2C, 2D, and 2E are compared, it is found that the residual SiO2 thickness is larger when the stage temperature shown in Table 2C is lower (stage temperature -20°C), and is smaller when the stage temperature shown in Table 2E is higher (stage temperature 20°C). Therefore, it is found that it is desirable to keep the stage 3 at a low temperature and obtain the necessary reaction temperature by irradiation with the IR lamp 60.

[0101] In this experiment, the temperature during irradiation by the second IR lamp 60 to remove the reaction layer ranged from 70°C to 95°C, as shown in Table 2B, but no particularly significant differences were observed within this temperature range. Furthermore, under the conditions of a stage temperature of -20°C and an IR output of 55%, which were relatively good performance conditions, the process of exhausting hydrogen fluoride gas and reaction products (step S104) in Figure 5 was performed for 120 seconds with Ar flowing at 1.4 L / min and the exhaust valve in the pressure adjustment means 14 fully open, rather than vacuum exhaust. As a result, it was found that this method was effective in reducing residues on the fine pattern compared to vacuum exhaust.

[0102] Next, using the process conditions (stage temperature -20°C) discussed above in FIG. 2A, the output of the IR lamp 60 in the first step (step S103) of forming the reaction layer was fixed at 55%, and the irradiation time (post IR (70%) time) of the IR lamp 60 (output 70%) in the second step (step 105) of removing the reaction layer was changed to 20 seconds, 30 seconds, 40 seconds, and 50 seconds, and 10 cycles of etching were performed according to the flow shown in FIG. 5.

[0103] Figure 2D shows the etched silicon nitride (PE-SiN) film thickness and etched silicon oxide (PE-SiO2) film thickness after 10 cycles, and the selectivity of silicon nitride to silicon oxide, as a function of the IR lamp irradiation time (post-IR) for the reactive layer removal in step 105. Figure 2D is a graph showing the etched silicon nitride and silicon oxide film thickness and selectivity for silicon nitride and silicon oxide films as a function of the IR lamp irradiation time in the second step of the second embodiment (stage temperature 0°C, total pressure 900 Pa, 10 cycles). Experimental results showed that when the IR irradiation for reactive layer removal was 20 seconds, the reactive layer was not successfully removed, and the film thickness could not be measured using an optical film thickness measurement device. As can be seen from Figure 2D, there was no significant difference in the results when the IR irradiation for reactive layer removal in step 105 was 30 to 50 seconds.

[0104] Here, as in the previous study, a sample was formed with 20 layers of alternating silicon nitride film 103 (40 nm thick) and silicon oxide film 102 (40 nm thick) to form a 200 nm slit-shaped space, and the etching characteristics of a fine pattern were evaluated using this sample. The experimental conditions were the same as those used in Figure 2D, and the slit sample was etched for 10 cycles. The results are shown in Table 2F. Table 2F shows the etching results when the irradiation time of IR for reaction layer removal (reaction layer removal IR) was changed.

[0105] [Table 2F]

[0106] When the IR irradiation time for reaction layer removal (reaction layer removal IR) was 30, 40, or 50 seconds, the results were good. In contrast, when the reaction layer removal IR was 20 seconds, as mentioned above, the reaction layer could not be removed and etching did not go well. From these results, it was found that if the temperature for reaction layer removal is too low, the reaction layer is not removed and etching does not go well.

[0107] As will be described later, the reaction product is thought to be primarily ammonium silicofluoride [(NH4)2SiF6]. Therefore, a certain level of temperature is required to decompose and volatilize it. However, if the temperature is too high, side reactions such as etching of the silicon oxide film 102 may occur, so the minimum necessary temperature is desirable. For these reasons, the second temperature for removing the reaction layer is preferably, for example, 70°C or higher and 110°C or lower, and more preferably 75°C or higher and 100°C or lower.

[0108] [Study on the thickness and composition of the reaction layer] Next, we investigated the thickness of the reaction layer. Here, we performed cycle processing under conditions equivalent to those shown in Figure 2C and Table 2E (stage temperature 20°C, 900 Pa, HF / Ar = 0.40 / 0.20 L / min, 60 seconds), varying the IR irradiation conditions for forming the reaction layer (the output of the IR lamp 60) from 30% to 50%. We omitted the IR irradiation for removing the reaction layer (the IR irradiation time for removing the reaction layer (reaction layer removal IR)). Specifically, in the flow chart of Figure 5, after exhausting hydrogen fluoride gas and reaction products (step S104), we proceeded to the next wafer cooling step (step S106) without removing the reaction layer by heating (step S105). Then, we repeated the cycle starting from the introduction of diluent gas (S102). (That is, multiple cycles were repeated, with the order of S102->S103->S104->S106 counted as one cycle.) Silicon nitride film samples were prepared after two, five, and ten cycles of IR-free reaction layer removal, and their cross sections were observed with a scanning electron microscope to measure the thickness of the reaction layer. The results are shown in Figure 2E. Figure 2E is a graph showing the thickness of the reaction layer on the silicon nitride film versus the number of cycles when the output of the IR lamp irradiated simultaneously with the HF supply was changed in the first step of the second embodiment.

[0109] Figure 2E shows the relationship between the thickness of the reaction layer and the number of cycles at a stage temperature of 20°C. The data is summarized for a case where the output of the IR lamp 60 that forms the reaction layer was varied from 30% to 50% (here, the IR output was set to 30%, 35%, 40%, 45%, and 50%). Table 2A summarizes the relationship between the IR output and the stage temperature. When the IR output was between 30% and 45%, the thickness of the reaction layer tended to saturate with the number of cycles. In contrast, when the IR output was 50%, the thickness of the reaction layer tended to increase significantly with the number of cycles. In terms of temperature, when the temperature was between 40°C and 60°C (IR lamp output between 30% and 45%), the thickness of the reaction layer tended to saturate, while when the temperature was 70°C (IR lamp output at 50%), the thickness of the reaction layer continued to increase with the number of cycles.

[0110] As shown in Table 2E, the etching results for fine patterns were good at a stage temperature of 20°C and an IR output of 35% and 40%. Considering the thickness of the reaction layer described above, if the reaction layer is too thick (at 50% IR output), the amount of reaction layer generated when decomposed and volatilized by the second IR irradiation is too large, possibly causing the shape of the adjacent silicon oxide film 102 to become thinner or deteriorate. Therefore, it is important to control not only the temperature for forming and removing the reaction layer, but also the amount of reaction layer generated. Considering Figure 2E, the thickness of the reaction layer is preferably 50 nm or less after 10 cycles. Therefore, in the first step, step S103, it is desirable to form a reaction layer of, for example, 5 nm or less per cycle.

[0111] The composition of the reaction layer was analyzed by X-ray photoelectron spectroscopy (XPS). As a result, the nitrogen (N1s) in the surface composition showed a peak at 402 eV, not the 395 eV of silicon nitride. This 402 eV peak was found to be attributed to ammonium salt. As for silicon (Si2P), a peak at 103 eV attributed to silicate was observed at 99 eV of silicon nitride, and a peak at 103 eV attributed to hexafluorosilicate SiF6 2- It is thought that the elemental ratio is similar to that of ammonium fluorosilicate [(NH4)2SiF6], where Si = 1, F = 6, and N = 2, but the elemental ratio of the surface of the reaction layer determined by XPS was Si = 1, F = 4.4, and N = 1.6. From the above, it is thought that the main component generated in the reaction layer is ammonium fluorosilicate [(NH4)2SiF6], and that the HF and NH3 produced when it decomposes and volatilizes may, depending on the conditions, etch the adjacent silicon oxide film. [Example]

[0112] [Etching method: Dry etching process flow 3] Next, a plasma-free etching process using hydrogen fluoride gas proposed in Example 3 of this embodiment, which differs in part from the etching process flow 1 shown in Example 1, will be described with reference to Figures 4, 6, and 9. Figure 6 is a flow chart of a silicon nitride film etching method according to an embodiment. Figure 9 is a time chart that schematically illustrates the flow of operations over time in the etching process according to the third example.

[0113] First, the wafer 2 is transferred into the processing chamber 1 through a transfer port (not shown) provided in the processing chamber 1, and then the wafer 2 is placed on the protrusion 56 on the wafer stage 3. In this case, the stage temperature is set to a predetermined temperature between 30°C and 55°C.

[0114] Thereafter, Ar gas for thermal conduction to the wafer 2 is supplied via the mass flow controller 52, the gas distributor 51, and the shower plate 23, thereby performing wafer heating on the stage in step S101 of FIG. 6. Because Ar gas serves both as thermal conduction to the wafer 2 and as a dilution gas for diluting the HF gas, steps S101 and S102 of FIG. 6 are performed simultaneously. The flow rate of Ar gas can be changed between when conducting heat to the wafer 2 and when used as a dilution gas. The flow of dilution Ar gas can be continued or stopped until the etching process is completed. N2 gas can also be used as an inert gas instead of Ar gas.

[0115] Next, in step S103 of Figure 6, a predetermined amount of HF gas was supplied to the processing chamber 1 for a predetermined time to form a reaction layer. Here, heating by an IR (infrared) lamp as shown in the flow of Figure 5 was not used, and only the temperature of heat transfer by the stage 3 was used. The temperature of the stage 3, i.e., the temperature of the wafer 2, is preferably, for example, 30°C or higher and 55°C or lower, and more preferably 35°C or higher and 50°C or lower. The film thickness of the reaction layer can be controlled by the temperature of the stage 3, the total pressure or HF partial pressure, the time, the number of repetitions, etc.

[0116] In this embodiment, the pressure used is preferably, for example, about 10 Pa to 1000 Pa, more preferably 50 Pa to 1000 Pa (50 Pa or more and 1000 Pa or less), and particularly preferably 300 Pa to 1000 Pa. The higher the pressure, the easier it is to form a reaction layer on the silicon nitride film, and the lower the temperature required for formation.

[0117] After forming the reaction layer for a predetermined time, the supply of HF gas is stopped and the HF gas remaining in the gas phase and the reaction products on the silicon nitride film as the reaction layer are exhausted in step S104 of Fig. 6. In step S104, Ar gas as a diluent gas is supplied during and after the exhaust, so that the reaction products can be exhausted more efficiently.

[0118] Next, heating is performed without flowing HF gas to remove the reaction layer (step S105 in FIG. 6). The heating temperature here is preferably 70°C to 110°C (70°C to 110°C), more preferably 70°C to 100°C (70°C to 100°C). Here, IR lamps 60 are used as the heating method. The heating method is not limited to this. For example, a method of heating the wafer stage 3 or a method of transferring the wafer to a separate heating-only device and performing the heating process may also be used. Ar gas or nitrogen gas may be introduced during irradiation with the IR lamps 60. The heating process may also be performed multiple times as needed. After heating, the wafer 2 is cooled (wafer cooling) in step S106. Steps S102 to S106 constitute one cycle, and this cycle is repeated N times (N is a positive integer). The cycle is repeated until the required etching depth is obtained, and then the flow in FIG. 6 ends.

[0119] Fig. 9 shows a time chart for the flow shown in Fig. 6. One cycle consists of a step of flowing HF gas and Ar (step of forming a reaction layer: S103) and a step of performing IR lamp heating without flowing HF gas (step of decomposing and volatilizing the reaction layer: S105), and by repeating this process N times, the silicon nitride film is etched.

[0120] [Etching result 3] Using the etching processing apparatus 100 used in Example 1 and the etching process flow of Figure 6, a process was investigated in which the temperature of stage 3 (stage temperature) was set to 20°C to 40°C, and IR heating was not performed in step S103, where HF / Ar was flowed. First, Ar was flowed at a flow rate of 1.4 L / min and 900 Pa for 60 seconds to conduct heat to the wafer 2. Then, while controlling the pressure at 900 Pa, HF was introduced at a flow rate of 0.40 L / min and Ar as a diluent gas at a flow rate of 0.20 L / min for 60 seconds. As a result, a reaction layer was formed on the silicon nitride film 103.

[0121] Thereafter, the exhaust valve in the pressure adjusting means 14 was opened 100% and the wafer 2 was evacuated for 120 seconds. This exhaust operation evacuated the fluorine gas and some of the reaction products. Next, with the set temperature of stage 3 remaining the same (20°C to 40°C), Ar was flowing at a flow rate of 0.50 L / min, and the IR lamp 60 was heated at 70% output for 30 seconds with the exhaust valve in the pressure adjusting means 14 opened 100%. This removed the reaction layer. After that, returning to the beginning, the wafer 2 was cooled with Ar flowing at a pressure of 900 Pa and a flow rate of 1.4 L / min for 60 seconds until it reached the same temperature as the temperature of stage 3. This series of processes was repeated 10 times according to the flow chart in Figure 6.

[0122] Figure 3A shows the etched film thickness of the silicon nitride film (PE-SiN), the etched film thickness of the silicon oxide film (PE-SiO2), and the selectivity of the silicon nitride film (PE-SiN) to the silicon oxide film (PE-SiO2) obtained after 10 cycles when the temperature of stage 3 was changed. Figure 3A is a graph showing the etched film thickness and selectivity of the silicon nitride film and the silicon oxide film when the stage temperature of the first step according to the third embodiment was changed.

[0123] As shown in Figure 3A, it was found that etching of silicon nitride film (PE-SiN) occurs depending on the stage temperature alone, and the etching amount of silicon nitride film (PE-SiN) is proportional to the stage temperature. In addition, etching of silicon oxide film (PE-SiO2) hardly occurs, and the selectivity is high for a single layer film.

[0124] Here, similarly to Examples 1 and 2, a sample in which a total of 20 layers of silicon nitride film 103 (40 nm thick) and silicon oxide film 102 (40 nm thick) were alternately formed was used to evaluate the etching characteristics of a fine pattern. The experimental conditions were the same as those used in FIG. 3A, and etching of the slit sample was performed for 10 cycles and 20 cycles. The results are shown in Table 3. Table 3 shows the results of etching a fine pattern under the conditions of FIG. 3A.

[0125] [Table 3]

[0126] Therefore, Table 3 shows the stage temperature and number of cycles, the recess depth (the amount of silicon nitride film etched minus the amount of silicon oxide film etched), the selectivity from the slit pattern results (the amount of silicon nitride film etched from its initial dimensions divided by the amount of silicon oxide film etched), and the remaining SiO2 thickness (thickness 108 of the tip of silicon oxide film 102 after etching shown in Figure 12 divided by the initial thickness 107 of silicon oxide film 102). Good etching conditions here are those in which the recess depth is relatively large, the selectivity is large, and the remaining SiO2 thickness is close to 1.

[0127] To make the evaluation results easier to understand, symbols such as ◎, 〇, △, and × are also shown in Table 3. The criteria are as shown in Table 1E above.

[0128] As a result, it was found that in both cases, the selectivity decreased when the number of cycles was increased to 20. In particular, when the number of cycles was increased, the corners of the silicon oxide film 102 tended to become rounded and the tip to become triangular, as shown by the shape 113 in FIG.

[0129] Although it is possible to etch the silicon nitride film 103 by reacting with HF at the temperature of the stage 3 alone, it was found that etching by a combination of cooling at a low temperature of the stage 3 and the IR lamp 60, as previously described in Examples 1 and 2, provides better selectivity and pattern shape. In other words, in the first step (step S103) and the second step (step S105), the stage 3 on which the wafer 2 is placed is kept at a low temperature of -50°C or higher and 0°C or lower, and then heated by the IR lamp 60, thereby obtaining a temperature of 30°C or higher and 55°C or lower in the first step and a temperature of 70°C or higher and 110°C or lower in the second step.

[0130] [Considerations regarding the thickness of the reaction layer] Next, similarly to Example 2, the thickness of the reaction layer was investigated. Here, the etching conditions (stage temperature 20°C to 40°C, 900 Pa, HF / Ar = 0.40 / 0.20 L / min, 60 seconds) shown in FIG. 3A and Table 3 were used. Cyclic processing was performed, but only the formation of the reaction layer was performed without IR irradiation for reaction layer removal. Specifically, in the flow of FIG. 6, after exhausting hydrogen fluoride gas and reaction products (step S104), the reaction layer was not removed by heating (step S105). The wafer was then cooled (step S106). After that, a cycle starting from the introduction of diluent gas (step S102) was repeated (i.e., multiple cycles were repeated, with the order of S101->S102->S103->S104->S106 counted as one cycle). Silicon nitride film samples were prepared by performing the reaction layer removal cycle without IR irradiation two, five, and ten times, respectively, and their cross sections were observed using a scanning electron microscope to measure the thickness of the reaction layer. The results are shown in Figure 3B. Figure 3B is a graph showing the thickness of the reaction layer on the silicon nitride film versus the number of cycles when the stage temperature in the first step of the third embodiment is changed.

[0131] Figure 3B shows the relationship between the thickness of the reaction layer and the number of cycles at stage temperatures of 30°C, 35°C, and 40°C. It can be seen that when the stage temperature is 30°C or 35°C, the thickness of the reaction layer tends to saturate with the number of cycles. When the stage temperature is 40°C, it was found that the thickness of the reaction layer tends to increase slightly with the number of cycles.

[0132] As described in Example 2, if the reaction layer formed is too thick, it is decomposed and volatilized by the second IR irradiation. When the amount of the reaction layer removed is too large, it can cause the shape of the adjacent silicon oxide film 102 to become thinner or deteriorate. Therefore, it is important to control not only the temperature for forming and removing the reaction layer, but also the amount of the reaction layer formed. Considering Figure 2E of Example 2, the thickness of the reaction layer is preferably 50 nm or less after 10 cycles. Therefore, in the first step, step S103, it is desirable to form a reaction layer of 5 nm or less per cycle. [Explanation of symbols]

[0133] 1: processing chamber, 2: wafer, 3: wafer stage, 11: base chamber, 12: quartz chamber, 13: discharge area, 14: pressure adjustment means, 15: exhaust means, 16: vacuum exhaust piping, 20: ICP coil, 21: high frequency power supply, 22: matching machine, 23: shower plate, 24: high gas dispersion plate, 25: top plate, 26: slit plate, 27: flow path, 30: electrostatic adsorption electrode, 31: electrostatic adsorption DC power supply, 38: chiller, 39: refrigerant flow path, 50: mass flow controller, 51: gas distributor, 54: valve, 55: He gas, 56: protrusion for proximity cooling, 60, 60-1, 60-2, 60-3: IR lamp, 61: reflector, 64: IR lamp power supply 70: thermocouple, 71: thermocouple thermometer, 72: IR light transmitting window, 73: power supply for IR lamp, 74: high frequency cut filter, 101: substrate, 102: silicon nitride film, 103: silicon oxide film, 104: opening, 105: laminated film, 106: etching amount of silicon oxide film relative to silicon nitride film, 111: edge of silicon oxide film after etching when selectivity is low, 112: diagram showing an example of the edge of silicon oxide film after etching, where the corners of the silicon oxide film remain rectangular while the film thickness of the silicon oxide film portion has become thinner, 113: diagram showing an example of the edge of silicon oxide film after etching, where the corners of the silicon oxide film have been rounded to form triangles.

Claims

1. 1. An etching method for dry etching a film structure including a silicon nitride film and a silicon oxide film, the film structure having been formed in advance on a wafer placed in a processing chamber, by supplying a processing gas into the processing chamber without using plasma, comprising: In a first step, hydrogen fluoride gas is reacted at a temperature of 30° C. or higher and 55° C. or lower to form a reaction layer on the silicon nitride film; After the first step, in a second step, heating is performed at a temperature of 70° C. or higher and 110° C. or lower without flowing the hydrogen fluoride gas, thereby volatilizing and removing the reaction layer formed in the first step; The first step and the second step are repeated a plurality of times to etch the silicon nitride film laterally from the end portion thereof; The etching method is characterized in that, in the first step and the second step, a stage on which the wafer is placed is set to a low temperature of -50°C or more and 0°C or less, and the wafer placed on the stage is heated, thereby obtaining a temperature of 30°C or more and 55°C or less in the first step and a temperature of 70°C or more and 110°C or less in the second step.

2. 2. The etching method according to claim 1, 10. The etching method according to claim 9, wherein the wafer is heated using a lamp.

3. 2. The etching method according to claim 1, An etching method, characterized in that the pressure in the first step is 50 Pa or more and 1000 Pa or less.

4. 2. The etching method according to claim 1, An etching method comprising a step of exhausting an inert gas while flowing the inert gas between the first step and the second step.

5. 2. The etching method according to claim 1, 10. An etching method, wherein the reaction layer formed in the first step has a thickness of 5 nm or less.

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